1. Field of the Invention
The present invention relates to a system in which audio to be recorded is transmitted using a wireless microphone. Further, the present invention relates to a receiver, a video camera and an audio mixer that constitute the system.
2. Description of the Related Art
In recent years, recording audio that is transmitted using a wireless microphone has become popular when gathering news materials and the like. FIG. 1 is a diagram showing an example of an external appearance of a wireless microphone. A wireless microphone transmitter (hereinafter referred to as a transmitter) 51 basically has a microphone and a modulator-transmitter transmitting a radio wave that is modulated by a audio signal from the microphone. A wireless microphone transmitter receiver (hereinafter, referred to as a receiver) 52 basically has a receiver-demodulator demodulating the audio signal after receiving the radio wave transmitted from the transmitter 51, and the demodulated audio signal is output to the outside of the receiver 52.
FIGS. 2A and 2B are diagrams each showing an example of audio transmission system using those transmitter 51 and receiver 52 for audio recording. In the example of FIG. 2A, the transmitter 51 is used by an interviewer. The receiver 52 is attached (or connected using a cable) to a VTR-incorporated video camera 53. Then, an audio signal input from the receiver 52 to the video camera 53 is recorded in the video camera 53 together with video that is captured by the video camera 53.
In the example of FIG. 2B, the transmitter 51 is used by an interviewer but the receiver 52 is connected to a stationary audio mixer 54 using a cable 55. Then, an audio signal input from the receiver 52 into the audio mixer 54 is mixed or switched in the audio mixer 54, and the audio signal output from the audio mixer 54 is recorded in a VTR, audio recorder which are not illustrated, or VTR-incorporated video camera such as the video camera 53 shown in FIG. 2A.
Hereupon, in the case where a wireless microphone including such transmitter 51 and receiver 52 is used, it is necessary to set a frequency of a radio wave used by the wireless microphone correspondingly to the circumstances of the site.
Specifically, a wireless microphone is typically made such that a frequency of a radio wave to be used can be set by selecting the frequency from a predetermined frequency band. However, there occurs interference when the same frequency being used by another device such as a wireless microphone used by others gathered around the site and a transmission system of a television broadcasting station located in the same area is selected as a frequency to be used at the site. Accordingly, it is necessary to select and set an available frequency that is not being used at the site when arrived at the site. Further, after starting, for example, news coverage, the frequency being used may need to be set again in response to fluctuation in the status of the radio wave due to a shift in the location and due to interference newly occurred by others gathered, and the like.
In the past, a frequency used by a wireless microphone is set at the site by operating an operation button for switching frequency that is provided in the transmitter 51 and receiver 52 to search an available frequency through a trial and error process.
In addition, only the followings are known in the past as the system including a wireless microphone and a video camera shown in FIG. 2A. There is a system in which only an audio signal (and a signal showing an RF level thereof) is output from a wireless microphone to a video camera, or a system in which an audio signal is output from a wireless microphone to a video camera and a control signal for controlling power on/off of the wireless microphone is output from the video camera to the wireless microphone (for example, refer to Patent Reference 1).    [Patent Reference 1] Japanese Published Patent Application No. 05-183788 (paragraphs 0021 through 0023, FIG. 1)